The vehicle is a 1989 standard cab Silverado with the 5.7L engine. About 7 months ago the compressor seized on it so I had to take it in. I took it to an A/C shop that I had been using for many years that was keeping it going as an R-12 system. This time they wanted to convert it to R134a since the compressor was shot and they were going to change out other components to get rid of debris (and their R12 price had really shot up). So it was converted and just about everything except the evaporator was now new. I'm not really sure how well it was working after that since it was still cool here (and my daughter was driving the truck). A couple of months went by and the evaporator decided to blow and puked dye out the drain hole. Insert more cash for parts, lots of labor and another recharge.

I was never satisfied with the air after the evaporator change (I didn't have a good feel for the R134 conversion to begin with since it was much cooler at the time). I didn't really get any satisfaction out of the shop as far as the mediocre vent temps. They stated that the pressures were fine and they didn't find anything wrong with any of the door controls. I got the typical line about these conversions not always working as well but I don't buy that they are this bad. I'm pretty much done with then now. They don't seem to be the same since the older guy retired who had given me great service in the past.

The truck was taken to another shop to get a second opinion. The guy there found the pressures to be fine and didn't find anything wrong with any of the doors or the duct work. He tried things such as pinching off the heater hoses, misting the condenser and etc but no real solutions.

After that I took a look at the doors and duct work myself and found no issues. I even tried things such as disconnecting the door motors with the recirc door and the blend door in the correct position for max cooling.

Some numbers:Today it was 105 degrees out with a reported humidity of 20%. I took a 30 minute drive with the vehicle reaching freeway speeds for many miles and the coolest vent temp was 83 degrees. I only noticed about a two degree rise when idling at lights vs moving at speed. Measuring the evaporator inlet and outlet at the firewall with a thermocouple came up with about 38 degrees after the drive. The accumulator was condensing with a lot of runoff.

My current theory is that it is evaporator related. I went so far as to pull the blower motor so that I could get in and feel the core. With the engine fired up and compressor running the evaporator doesn't feel like it is getting very cool even though the inlet and outlet temps under the hood are around 38 degrees. To me it seems like the flow is from the inlet tube, it then passes along the bottom of the core and then it shoots straight up the front wall to the outlet at the top. It just feels like the front wall is the only part of the core that is getting cool with the majority of the core being much warmer. Is there anything that might explain the uneven cooling of the evaporator core?

May have missed something in that read but seems all problems really began with evaporator change out. I doubt the replacement fits properly in position or sealed up well such that air flows around it which is what you are getting at panel vents not what the evap could and is doing alone.

Heat wins over A/C so anything not sealed + broken parts possible for heater box (whole duct housing for evap and heater) would be a patch not brand new or good used by now very hard to find one any better probably.

In short - air gets around the new evaporator that doesn't fit properly or wasn't installed properly,

Sounds like evaporator was built wrong-- seen it twice in my life- you have done all the right things- and tested correctly- so pull out evaporator and study the design, there are tabs that show the "blanks" that reverse the flow direction- should be 5 sections south, 5 sections north, 5 sections south- with two "blanks" between direction changes- Chances are good your tabs are on same end, (reversed) built by wrong by goofy assembler....probably texting while assembling....

Last one I saw was probably 20 yrs ago-- I could hold it up and see right through it- inlet to outlet....

I would say that the evaporator is otherwise partially clogged. For the record, we've been hit twice this year with bad evaporators, in a 2013 Ram and a 2008 Avenger. Chinese curse I guess. Unfortunately, there is not much to choose from.

Same reason when you drop a tool it will find the hardest place possible to retrieve it!

Nacho by leaps and bounds would know of a defect rate more than I could with parts. Long done with this stuff but now or back when I'm in such a temperate climate that an older vehicle that is used year round would be so rusted in general it would be scrapped just for that never mind if otherwise fine.

Folks wouldn't spend the $$ or just effort if parts were free for just A/C most can live without yet it gets as hot here as almost anywhere just for short times usually just mid day.

Haven't had the joy of "Dash Diving" I'll call it on this truck's particular dash or HVAC box as none failed that were destined to be my work.

I'm at a bit of a loss as how to verify this as defective short of putting another in so think I'd try like all get out to measure the temps at locations I could get to with it operating to see by infrared thermos (fussy dang things) just what is happening where to condemn it.

Have to leave the final call to you and your observations and can only say that if you were just there it's usually much faster the second time both familiar with it and if really annoying to get at you know what worked.

These things simply have to seal tight whatever it takes that will last.

IDK - it was ACProf here who cut a condenser open on a vehicle known from new and found a blockage in it unknown till it broke for another reason and since the A/C never worked better!

I decided to change out the evaporator over the weekend after having a friendly shop evacuate the system. Me and my daughter dis-assembled the air box, put in the new evaporator, added a fresh air seal and got it all buttoned up nice and tight. Today I took it over to get it recharged and now we have nice cold air again. I knew that the R134 conversion couldn't possibly be as bad as what we were getting with the old evaporator especially with a small cab pickup that had excellent AC to begin with.

While the truck was getting recharged I spent a little time dissecting the old evaporator. It turns out that both of the blocking plates were in the top tube and the bottom tube had none. One of the plates had been put in upside down at the factory! The resulting refrigerant flow was exactly what I was expecting based upon my feel test of the evaporator with the blower motor removed. It was entering the evaporator at the bottom and then traveling all of the way across to the other wall and then shooting up to hit the outlet tube at the opposite top side. There wasn't a plate in the bottom anywhere to force it up into a zig-zag through the evaporator. I also couldn't find any external indicators on the evaporator to show where the blocking plates are so you couldn't tell by inspection. The new evaporator had notches in the blocking plates to show exactly where they are (one in the top tube and one in the bottom).

Now it is off to the initial shop to see if they will at least reimburse me for the piece of garbage evaporator.

OK - Seems like you are all set now except dealing with the installation of a bad evaporator, wrong one or hacked in job of some sort?

I didn't re-read whole thread and really don't need to. These vehicles with small cabs will convert and be fine without too much fan-fare at all just slightly less powerful A/C you may not even notice.